Up until eighth grade in my school district 64% or less was an F, 65-69% was a D, 70-81% was a C, 82-91% is a D, and 92% or more was an A. In secondary school, 69% or lower became an F, 70-75% was a D, 76-84% was a C, 85-92% was a B, and 93% or more was an A. It may have become more relaxed since I left. However, I have never seen an A being less than 90% in any system.